Method and a device for changing the compression ratio in an internal combustion engine

ABSTRACT

A process and apparatus for setting the compression ratio of an internal combustion engine by changing the relative distance between the axis of rotation of the engine crankshaft and the engine cylinder head surface delimiting the end of each cylinder in the engine. Relative displacement between the rotational axis of the crankshaft and the cylinder head is effected along a predetermined path that has components both parallel and transverse to the longitudinal axis of each of the engine cylinders. The crankshaft is held with its rotational axis stationary in relation to the engine mountings and the vehicle in which the engine is mounted, and the cylinder head is displaced along the predetermined path together with the cylinder.

The invention relates to a process for setting the compression ratio inan internal combustion engine by changing the relative distance betweenthe axis of rotation of the engine crankshaft and the engine cylinderhead surface delimiting the end of each cylinder in the engine, and adevice for carrying out said process.

Conventional internal combustion engines work with a fixed compressionratio which is determined by the dimensions of the engine components. Inorder to change the compression ratio, the engine must be disassembledand components with other dimensions must be built into the engine, forexample pistons of another height or a cylinder head with another designof the combustion chamber. This means that the compression ratio cannotbe changed simply.

In certain cases, there is a need to change the engine compression ratioto adapt it to fuels of varying qualities, and different proposals havebeen made to achieve this. All of these, however, only provide thepossibility of a relatively small change in the compression ratio.

The purpose of the present invention is to provide a device which makespossible a great change in the compression ratio in an internalcombustion engine, so that the compression ratio can, for example, bechanged within the range 4-40, during operation. This means that thecompression ratio can be changed depending on the current engineoperating conditions, so that the engine efficiency can be improved,especially under partial load, so that the engine power range can beincreased. In order to fully exploit these possibilities, the supply ofair and fuel to the engine should also be controlled in relation to theset compression ratio. For this, suitable valve systems are required andsystems for supplying air and fuel, but these systems do not constituteany part of the present invention and therefore will not be described inmore detail here.

According to the invention, rotation of the adjustment discs displacesthe rotational axis of the crankshaft in two dimensions, namely, on onehand, parallel to the longitudinal axis of each engine cylinder, and, onthe other hand, perpendicular thereto. In this manner, there isprovided, in addition to a change in the compression ratio, also alateral displacement of the crankshaft, which means that the angularrelationship for the crankshaft in each cylinder is changed.

The invention will be described in more detail below with reference tothe accompanying drawings, of which:

FIG. 1 is a schematic end view of an internal combustion engine with adevice according to one embodiment of the invention,

FIG. 1a is a schematic end view of a somewhat modified internalcombustion engine according to FIG. 1 and shows the suspension of theengine,

FIG. 2 shows a schematic section through the engine according to FIG. 1perpendicular to the rotational axis of the crankshaft in its positionfor the smallest compression ratio,

FIG. 3 shows a section corresponding to FIG. 2 but in its position forthe highest compression ratio,

FIG. 4 shows a schematic longitudinal section through the engineaccording to FIG. 1, essentially through the longitudinal axis of thecylinders, in the position for the smallest compression ratio,

FIG. 5 shows a section corresponding to FIG. 4, but in its position forthe highest compression ratio,

FIG. 6 is a schematic, partially cut-away end view of an engineaccording to another embodiment of the invention,

FIG. 7 shows a schematic longitudinal section through a portion of theengine according to FIG. 6, essentially through the longitudinal axis ofthe cylinders, in the position for the smallest compression ratio,

FIG. 8 shows a section corresponding to FIG. 7, but in the position forthe highest compression ratio,

FIG. 9 is a schematic view of a drive device for a cam-shaft in anengine according to the invention.

The drawings show an internal combustion engine which is equipped with adevice according to the invention. The internal combustion enginecomprises in a known manner an engine block 1 and a cylinder head 2. Theengine block 1 is closed at its bottom in a known manner by means of anoil pan 3 and has a number of cylinders 4, in each of which there isarranged a piston 5 for reciprocal movement. Each piston 5 is connectedby means of a piston rod 6 (shown as a heavy dash-dot line in FIGS. 2-5)to a crankshaft 7, which is mounted in the engine block 1 for rotationabout a rotational axis 7a.

The cylinder head 2 is made in a known manner with a combustion chamber8 for each cylinder 4 and inlet and outlet ducts to permit gas exchangein the combustion chamber 8. Of these ducts, FIGS. 2 and 3 show an inletduct 9, the communication of which with the combustion chamber 8 iscontrolled by means of a valve 10, which is in turn controlled by meansof a valve mechanism 11. The valve mechanism 11 constitutes no part ofthe present invention and therefore will not be described in more detailhere. The valve mechanism 11 is in turn driven by the crankshaft 7, andthis drive device will be described in more detail below.

In the cylinder head 2, there is also a spark plug 12 for each cylinder4, which, in a known manner, extends with its inner end into thecombustion chamber 8. The spark plug 12 and the ignition system, ofwhich it is a part do not constitute a part of the present inventioneither and therefore will not be described in more detail here. If theengine is a diesel engine, there is of course no spark plug, there beinginstead a jet for fuel injection.

The crankshaft 7 is, according to the invention, mounted for rotation incrankshaft bearings in the engine block 1. Each crankshaft bearingcomprises, in the embodiment according to FIGS. 1-5, an adjustment disc13, 14 or 15, as is best shown in FIGS. 4 and 5. Each of the adjustmentdiscs 13, 14 and 15 is thus provided with a bearing opening 16, 17 and18, respectively, and the crankshaft 7 is mounted for rotation in thesebearing openings. The bearing openings 16, 17 and 18, respectively, areexcentrically arranged in the adjustment discs 13, 14 and 15,respectively, as is best shown in FIGS. 2 and 3. The adjustment discs13, 14 and 15 are in turn mounted for rotation in bearing openings 19,20 and 21 an the engine block 1.

The adjustment discs 13 and 15 located at the ends of the engine arealso made with bearing races 22 and 23, respectively, which are arrangedconcentrically to the rotational axis 7a of the crankshaft 7. On thebearing races 22 and 23, bearings 24 and 25, respectively, are arranged,said bearings being arranged in bearing openings 26 and 27,respectively, in the ends 28 and 29, respectively, of a frame 30. Theframe 30 surrounds the engine block 1 and supports, via the adjustmentdiscs 13 and 15, the entire engine. The frame 30 is intended to bepermanently mounted, and a clutch and a gear box can be connected in aknown manner to the end 29 of the frame 30.

When the adjustment discs 13, 14 and 15 are turned by means of amechanism which will be described in more detail below, the engine block1 and the cylinder head 2 will be displaced relative to the frame 30. Inorder for this displacement to be effected in the desired manner, theengine block 1 is guided relative to the frame 30 in the manner shown inFIG. 1a. The oil pan 3, or the corresponding lower portions of theengine, supports a guide pin 61 for this purpose, which is parallel tothe crankshaft 7 and runs in a guide groove 62, which is arranged in theframe 30 (see also FIGS. 4 and 5). The guide groove 62 is shaped so thatthe engine block 1 and the cylinder head 2 are displaced in the desiredpath. FIG. 1a also shows two engine mountings 63 which are arranged onthe frame 30 for suspending the same relative to the vehicle, in whichthe engine is mounted. Only very small portions 64 of the vehicle areshown at the engine mountings 63.

The adjustment discs 13, 14 and 15 are provided with toothed segments31, 32 and 33, respectively, which are concentric to the bearingopenings 19, 20 and 21, respectively, in the engine block 1. The toothedsegments 31, 32 and 33 are in engagement with gears, of which one isshown at 34 in FIGS. 2 and 3, on a hollow adjuster shaft 35 which ismounted for rotation in the engine block 1. The adjuster shaft 35 isthus made as a part of a hydraulic rotational cylinder, and it is shownin the vicinity of its end positions in FIGS. 2 and 3.

As the adjustment discs 13, 14 and 15 are rotated by means of the gears34 on the adjuster shaft 35, the axis of rotation 7a of the crankshaft 7will be displaced relative to the engine block 1 and the cylinder head2. In the embodiment shown in the drawings, this occurs by the engineblock 1 and the cylinder head 2 being displaced relative to thecrankshaft 7 while the rotational axis 7a of the crankshaft 7 is fixedrelative to the frame 30. As the adjustment discs 13, 14 and 15 arerotated, the surface of the cylinder head 2 which delimits thecombustion chamber 8 in the cylinder 4 is displaced toward or away fromthe axis 7a of the crankshaft 7. This means that the upper end positionof the piston 5 is changed, which in turn changes the volume of thecombustion chamber 8 when the piston 5 is at its upper end position.This means also that the compression ratio of the engine is changed.FIGS. 2 and 4 show the piston 5 in its upper end position with therotational axis 7a of the crankshaft 7 located at its greatest possibledistance from the cylinder head 2, and in FIGS. 3 and 5, the piston 5 isshown in its upper end position with the rotational axis 7a of thecrankshaft 7 located at its smallest possible distance from the cylinderhead 2. This means that FIGS. 2 and 4 show the lowest possiblecompression ratio, while FIGS. 3 and 5 show the highest possiblecompression ratio.

FIGS. 6-8 show an engine according to another embodiment of theinvention. This differs in certain respects from the engine according toFIGS. 1-5. The components, which are common to the two embodiments, are,however, labelled in all the Figures with the same referencedesignations.

In the engine according to FIGS. 6-8, the crankshaft 7 is mounted forrotation in bearings 36-38 in an engine block 39, which in this casedoes not include the engine cylinders 4. These are instead arranged in acylinder bank 40, which is arranged above the engine block 39 and onwhich the cylinder head 2 is mounted.

The cylinder bank 40 is joined to the engine block 39 by means of theadjustment discs 13-15, which are mounted for rotation about thebearings 36-38, and connection discs 41-43. The connection discs 41-43are mounted on the outer circumference of each adjustment disc 13-15 andare joined to the cylinder bank 40 by means of screws 44.

The adjuster shaft 35 in the embodiment according to FIGS. 6-8 is madewith tooth segments 45 for engagement with the tooth segments 31-33 ofthe adjustment discs 13-15, as is best revealed in FIG. 6.

As the adjustment discs 13-15 are turned, the cylinder bank 40 and thecylinder head 2 will be displaced relative to the engine block 39, sothat one obtains the desired change in the compression ratio in a mannercorresponding to that described in connection with the embodimentaccording to FIGS. 1-5. In FIG. 7, the crankshaft 7 is shown with itsrotational axis 7a located at the greatest possible distance from thecylinder head 2, while FIG. 8 shows the rotational axis 7a of thecrankshaft 7 located at the smallest possible distance from the cylinderhead 2. This means that FIG. 7 shows the smallest possible compressionratio, while FIG. 8 shows the highest possible compression ratio.

The embodiment shown in FIGS. 6-8 is also possible to use with engineswith several banks of cylinders, for example V-engines and boxerengines, where all the cylinder banks can be manoeuvred by means of asingle adjuster shaft.

FIGS. 1 and 6 also show a device for driving an intermediate shaft 46arranged in the cylinder head 2, said intermediate shaft driving in turnthe valve mechanism 11. The intermediate shaft 46 is driven by thecrankshaft 7 by means of a drive chain 47 which is shown with dash-dotlines. The drive chain 47 is driven by the crankshaft 7, and when thecylinder head 2 is displaced relative to the crankshaft 7, by theadjustment discs 13, 14 and 15 being turned, the distance between theintermediate shaft 46 and the crankshaft 7 will of course be changed. Inorder to keep the drive shaft 47 always taut, it is led on either sideof the crankshaft 7 over equalizer wheels 48. Each equalizer wheel 48 ismounted on an arm 49, one end of which is pivoted about a point 50 whichis fixed relative to the crankshaft 7. The other end of each arm 47 ispivotally connected to a point 51 which is moveable together with thecylinder head 2. In this manner, regardless of the position of therotational axis 7a of the crankshaft 7 relative to the cylinder head 2,the drive chain 47 will be held taut, and this is done without anychange in the relative rotational position between the crankshaft 7 andthe intermediate shaft 46.

As can be seen in FIGS. 1 and 6, the intermediate shaft 46 drives asecondary chain 52 or 53, respectively, which in turn drives the valvemechanism 11. The secondary chain 52 or 53, respectively, is notaffected by the movement of the cylinder head 2 relative to thecrankshaft 7, and therefore no equalizer devices for the secondary chain52 or 53, respectively, are required.

FIG. 9 shows an alternative embodiment of the driving device for thevalve mechanism 11. In this embodiment, the crankshaft 7 drives a driveshaft 54 in the valve mechanism by means of a single drive means in theform of a toothed belt 55 with teeth on both sides. The toothed belt 55is led over equalizer wheels 56 on both sides of the crankshaft 7. Theequalizer wheels 56 are, in a manner corresponding to the embodimentshown in FIGS. 1 and 6, mounted on arms 57. One end of each arm ispivoted to a point 58 which is fixed relative to the crankshaft 7, whilethe other end of each arm 57 is pivotally joined to a point 59 which isfixed relative to the cylinder housing 2. There is also a tensioningwheel 60 which is arranged to keep the toothed belt 55 under suitabletension to avoid slack. FIG. 7 shows one end position for the arms 57with solid lines, while the other end position is shown with dash-dotlines. It should also be noted in this context that the toothed belt 55can be replaced by a chain if this should be desirable.

As is particularly evident from FIGS. 2 and 3, rotating the adjustmentdiscs 13-15 displaces the cylinder head 2 not only parallel to thelongitudinal axis of the cylinder 4, but also perpendicular thereto. Thedisplacement is thus effected in two dimensions. This changes of coursealso the angle of the piston rod 6 relative to the longitudinal axis ofthe cylinder 4.

This change in the angle of the piston rod 6 relative to thelongitudinal axis 4a of the cylinder 4 is revealed by a comparison ofFIGS. 2 and 3, which both show the position when the piston 5 is in itsupper end position. In FIG. 2, the cylinder head 2 is displacedlaterally relative to the longitudinal axis of the cylinder 4. Thismeans that the piston 5 during the last portion of the compressionstroke will move a longer distance for each degree of a turning of thecrankshaft 7 than in the first portion of the subsequent power stroke.In this manner, it is possible to increase the efficiency of the engine.

In FIG. 3, the cylinder head 2 is displaced a smaller distance relativeto the longitudinal axis of the cylinder 4, and it is of course possibleby suitable dimensioning of the adjustment discs 13-15 and suitableplacement thereof to achieve a lateral displacement of the cylinder head2 which provides the desired pattern of movement of the piston 5 atvarious compression ratios.

That described above also applies, of course, to the embodiments shownin FIGS. 6-8.

The device described above, as was mentioned previously, makes itpossible to change the compression ratio of the engine within a widerange. This change can be done when the engine is operating, and bysuitable control of the movements of the adjuster shaft 35, it ispossible to change the compression ratio of the engine in such a mannerthat it is adapted to the current load conditions. This change iseffected by means of a single operating means in the form of an adjustershaft, and this applies regardless of the number of cylinders in theengine and regardless of the number of cylinder banks and theirplacement.

I claim:
 1. In a process for setting the compression ratio of aninternal combustion engine by changing the relative distance between theaxis of rotation of the engine crankshaft and the engine cylinder headsurface delimiting the end of each cylinder in the engine, the relativedisplacement between the rotational axis of the crankshaft and thecylinder head being effected along a predetermined path that hascomponents both parallel to a plane containing the longitudinal axis ofeach of the engine cylinders and perpendicular to said plane;theimprovement comprising holding the crankshaft with its rotational axisstationary in relation to the engine mountings and the vehicle in whichthe engine is mounted, and displacing the cylinder head along thepredetermined path together with the cylinder.
 2. A process according toclaim 1, wherein the predetermined path is a circular arcuate path.
 3. Aprocess according to claim 1, wherein the predetermined path is anessentially straight path, which is disposed at an acute angle to thelongitudinal axis of each cylinder.
 4. In a device for setting thecompression ratio in an internal combustion engine by changing therelative distance between the rotational axis (7a) of the enginecrankshaft (7) and the engine cylinder head (2) surface delimiting theend of each cylinder (4) in the engine, the crankshaft (7) being mountedfor rotation in eccentrically placed bearing openings (16-18) incircular adjustment discs (13-15), which are rotatably mounted inbearing openings (19-21) in the engine block (1), a rotating device(31-35) being coupled to the adjustment discs (13-15) for simultaneousrotation thereof relative to the engine block (1); the improvementwherein a said adjustment disc (13, 15) is mounted at each end of thecrankshaft (7), each of said adjustment discs (13, 15) having a bearingrace (22, 23) concentric to the bearing opening (16-18), by means ofwhich race the adjustment disc (13, 15) is rotatably mounted in a frame(30), and wherein the engine block (1), by means of at least one guidemeans, is joined to the frame (30) for controlled displacement relativethereto upon rotation of the adjustment discs (13-15) by means of therotating device (31-35), which is fixed relative to the engine block(1).
 5. In a device for setting the compression ratio in an internalcombustion engine by changing the relative distance between therotational axis of the engine crankshaft and the engine cylinder headsurface delimiting the end of each engine cylinder;the improvementwherein the crankshaft (7) is mounted for rotation in bearings (36-38)in the engine block (39), circular adjustment discs (13-15) mounted ineccentrically placed bearing openings for rotation in the engine block(39), at least one cylinder bank (40) housing the engine cylinders (4)and on which the cylinder head (2) is mounted, said cylinder bank beingjoined to connection discs (41-43) which are mounted on the outercircumference of the adjustment discs (13-15), and a rotating device(31, 35, 45) coupled to the adjustment discs (13-15) for simultaneousrotation thereof to move the cylinder head (2) relative to the engineblock (39).
 6. Device according to claim 4, wherein the rotating deviceconsists of a hydraulic rotational cylinder (35) with gears or toothedsegments (34, 45) in engagement with toothed segments (31-33) on each ofthe adjustment discs (13-15).
 7. Device according to claim 5, whereinthe rotating device consists of a hydraulic rotational cylinder (35)with gears or toothed segments (34, 45) in engagement with toothedsegments (31-33) on each of the adjustment discs (13-15).
 8. Deviceaccording to claim 4, wherein the crankshaft (7) drives a valvemechanism (11) in the cylinder head (2) by means of at least one drivemeans in the form of a chain (47) or a toothed belt (55), and whereinthe drive means (47, 55) is led over two equalizer wheels (48, 56),which are arranged for displacement corresponding to the displacement ofthe cylinder head relative to the rotational axis (7a) of the crankshaft(7) without any mutual rotational movement between the crankshaft (7)and the valve mechanism (11).
 9. Device according to claim 5, whereinthe crankshaft (7) drives a valve mechanism (11) in the cylinder head(2) by means of at least one drive means in the form of a chain (47) ora toothed belt (55), and wherein the drive means (47, 55) is led overtwo equalizer wheels (48, 56), which are arranged for displacementcorresponding to the displacement of the cylinder head relative to therotational axis (7a) of the crankshaft (7) without any mutual rotationalmovement between the crankshaft (7) and the valve mechanism (11).